Closed hydraulic system



Feb. 5, 1957 E. w. SPANNHAKE 2,780,065

' CLOSED HYDRAULIC SYSTEM Filed July 20, 1955 V REL RESERVOIR L HYDRAULIC INVENTOR. ERNST W SPAN NHAKE ATTORNEY United States Patent CLOSED HYDRAULIC SYSTEM Ernst W. Spannhake, Peoria, 111., assignor to LeTourneau- Westinghouse Company, Peoria, Ill., a corporation of Illinois Application July 20, 1955, Serial No. 523,307

Claims. (Cl. 60-52) This invention relates to a hydraulic system, especially to a closed hydraulic system in which one element of the system produces volume variations for which compensation must be made by another element.

There are a great many industrial applications of hydraulic actuators or motors in which cylinder and piston mechanisms are used and in which it is necessary that the motor be double-acting-i. e., be capable of producing motion in both directions. Apparatus of this type presents a problem inasmuch as the presence of a piston rod in the rod end of the motor and no rod in the head end of the motor makes for a difference in the quantity of fluid which it takes to fill one end of the cylinder as against the quantity or volume required to fill the other end. In a closed hydraulic system, which is necessary to avoid cavitation due to the speed of movement, some provision must be made to accommodate the resulting volume diflerentials.

It is accordingly an object of this invention to provide a simple and inexpensive closed hydraulic system using a double-acting cylinder and piston type of motor in which the volume differential caused by the piston rod is automatically compensated for by another element of the system. The manner in which this and other objects are achieved will be apparent to those skilled in the art by a careful study of the following description and the annexed drawing.

. The sole figure of the drawing shows schematically a preferred embodiment of the inventiomin which a positive displacement reversible constant delivery pump is shown at 2 and is provided with a pair of ports 4 and 6.

A hydraulic actuator or, motor of any suitable type may be provided; in the embodiment shown, a motor 8 is shown as consisting of a cylinder 10, a piston 12 mounted for reciprocation in the cylinder, and a piston rod 14 connected to the piston and extending out through end 16 of the cylinder which for convenience is referred to as the rod end of the cylinder. The oppositeend 18 of the cylinder is for convenience referred toas the head end.

Conduit means are connected with the two ports 4 and 6 of pump 2 and serve to connect the pump with the head end 18 and rod end 16 of the motor 8. In the embodiment shown, a conduit 20 connects port 4 of the pump with rod end 16 of the cylinder, while conduit 22 connects port 6 of the pump with the head end 18 of the cylinder.

A compensator indicated generally at 24 may be termed broadly as means capable of producing volume if the pressure in the conduit means falls below the pump supply pressure and capable of taking on fluid when the pressure in the conduit means goes higher than pump supply pressure. More specifically, compensator 24 consists of a two-part cylinder, one part being ShOWn at 26 and the other part shown at 28. Stop means are provided between the ends of the two-part cylinder. In the preferred embodiment shown, the stop means consists of an annulus 30 provided with opposed seats 32 and 34 against which the ends of parts 26 and 28 respectively seat. Heads 36 and 38 engage the outer ends of parts 26 and 28 respectively. The parts of the compensator are held together by bolts 46 and 42 engaging heads 36 and 38 respectively and the annulus 30. Seats 32 and 34 provide shoulders 44 and 46 on faces 32 and 34 respectively, these shoulders serving as stops for a purpose to be described.

Pistons 48 and 50 are reciprocable in parts 26 and 28 respectively between ends 36, 38 and stops 44, 46 respectively. Pistons 48 and 50 are resiliently biased apartby any suitable means, as for example by gas pressure or some conventional mechanical expedient. In the embodiment shown, a coil spring 52 is shown as extending through the central opening of the annulus which forms stop 38, the ends of spring 52 engaging the inner faces of pistons 48 and 50. The pistons will be suitably packed against fluid leakage as indicated at 54 and as will be understood by those skilled in the art.

The opposite ends of the compensator 24 are connected with the conduit means referred to above as joining the pump 2 and the hydraulic motor 8. Thus, a branch conduit 56 communicates conduit 22 with the interior of one end of the two-part cylinder by means of a suitable passage in the head 36; similarly, a branch conduit 58 connects conduit 20 with the other end of the cylinder through a passage in head 38.

The customary precautions against excessive pressures arising in the system must of course be taken. Toward that end, and because the pump 2 is reversible, two branch conduits provided with suitable relief valves permit by-passing of the'hydraulic motor. Thus, a branch conduit 60 having therein a conventional relief valve 62 extends between conduit 22 and branch conduit 58. Similarly, branch conduit 64 having therein a relief valve 66 extends between conduit 22 and branch conduit 58. Relief valves 62 and 66 are of course arranged to open in opposite directions as indicated by the arrows on the drawing.

Inasmuch as means must be provided in order to charge the system initially with fluid, a reservoir is indicated at 68. Reservoir 68 is connectible with the system by way of a branch conduit 70 and a three-way valve 72. Three-way valve 72 is provided in the branch conduit 58. In the position shown in the drawing, valve 72 blocks communication between reservoir 68 and branch conduit 58, because this is the position of valve 72 for normal operation of the system.

The mode of charging the system with hydraulic fluid will be understood by those skilled in the art and need not be discussed in detail.

Operation For a better understanding of the operation of the illustrated embodiment of this invention, let it be assumed that piston 12 moves through its entire stroke during normal operation. Let it be further assumed that piston 12 is as far as it can go to the left as seen in the drawing, and that the pump 2 is being driven in the direction to pump hydraulic fluid out through port 6 and thus of course to draw hydraulic fluid in at the same rate through port 4.

For most eflicient operation, the system is of course designed so that no fluid passes through relief valves 62 and 66 for normal operation. Thus, motor 8 takes all of the fluid discharged by pump 2 through port 6, and

it does so as piston 12 moves to the right as seen in the drawing. As piston 12 moves toward the right, fluid is discharged from cylinder 10 by way of rod end 16 through conduit 20 to port 4, which for this phase of the operation serves as the supply port.

Thus it will be seen that cylinder 14? receives a given volume of fluid in moving through its entire working stroke, that is to say, from its extreme left position to its extreme right position having reference to the orientation of parts shown in the drawing. Because of the presence of piston rod 14 on the right face of piston 12, the volume discharged by cylinder ltl from rod end 16 is diflerent from the volume received by cylinder lit at head end 18 from conduit 22. Furthermore, this different volume is smaller than the given volume by a predetermined amount. In the type of motor shown in the illustrated embodiment, the aforesaid predetermined amount is determined by the volume occupied by that portion of piston rod 14 which is surrounded by hydraulic fluid when piston 12 is in its extreme leftward position.

Accordingly, as piston 12 moves toward the right through this portion of its working stroke, a volume of fluid is discharged into conduit Zflwhich is smaller than the volume passing through conduit 22. Inasmuch as fluid is passing through ports 4 and 6 of pump 2 at substantially equal rates, the fluid discharged by cylinder 16 into conduit 20 is insufiioient to supply the pump 2 and the deficiency must be made up by compensator 24.

Referring now to compensator 24, it will be understood by those skilled in the art that the high pressure in conduit 22 is sufflcient to keep piston 48 in its extreme right position in cylinder part 26, namely seated against the stop provided by shoulder 44 on stop means 30. This is the position of the piston shown in the drawing.

Because the spring 52 between pistons 48 and G is under a substantial compression, piston 50 moves to the right as seen in the drawing as soon as any volume deficiency appears in conduit 20. This is of course manifested by a supply pressure drop in branch conduit 58, permitting hydraulic fluid to be discharged from compensator 24 into conduit 2th by way of branch conduit 58 to make up the volume deficiency created by piston rod 14.

Thus, for the working stroke just outlined (left to right motion of piston 12), compensator 24 supplies the volume deficiency in the predetermined amount and prevents cavitation in the pump.

Let it now be assumed that the operator wishes to move the hydraulic motor 8 through the reverse working stroke. To do so, he reverses the direction of operation of pump 2. Immediately, conduit 20 becomes the high pressure conduit or pump discharge conduit, and conduit 22 be comes the pump supply conduit. Presumably, the resistance to movement of piston 12 offered by the load connected to the hydraulic motor 8 is such that piston 50 must first be seated against shoulder 46 of stop 30. Accordingly, fluid discharged through port 4 of pump 2 first goes to compensator 24, moving piston St to its extreme leftward position (this being the position it occupies in the drawing) before there is any movement of piston 12. Inasmuch as piston 12 is stationary during this leftward movement of piston 50, cylinder 10 is not discharging any fluid into conduit 22 and is thus not supplying pump 2 with any fluid for port 6 which is now serving as the supply port. Therefore, for that stage of the operation during which piston 52 moves from its posit-ion near head 38 to the position shown in the drawing, fluid must be supplied to conduit 22 and port 6 by compensator 24. This it does by piston 48 moving leftward under the influence of spring 52, expelling hydraulic fluid from compensator 24 to conduit 22 by way of branch conduit 56. Thus, for this first portion of the reverse working stroke, pistons 48 and 50 move practically as a unit toward the left.

As soon as piston 50 engages shoulder 46, compensator 24 is no longer able to receive any of the fluid which is being discharged by pump 2. At this point, the pressure in conduit 26 increases sufliciently to overcome the resistance which the load offers to movement of piston 12, whereupon piston 12 begins to move from its extreme right position to its extreme left position.

As the piston moves from right to left, hydraulic fluid is of course discharged by cylinder- 10 in a greater amount than it is received y c l nder 1 Asa u, er the entire working stroke, the volume discharged is greater than the volume received by the predetermined amount re ferred to above, this being the volume taken up by that portion of piston rod 14 which is surrounded by hydraulic fluid when piston 12 is in its extreme leftward position.

Inasmuch as ports 4 and 6 of the pump pass hydraulic fluid at equal rates, it will be seen that cylinder 10 is discharging fluid faster than it can be received by pump 2. The excess passes through branch conduit 56 into the left end of compensator 24 and moves piston 48 back again to its position against shoulder 44, so that when the operator is ready to begin the working stroke by which piston 12 moves from its extreme leftward position to the right, the elements of compensator 24 occupy the position shown in the drawing.

It will of course be understood by those skilled in the art that compensator 24 is designed to provide more than the predetermined amount of piston rod 14 as defined above in order to take care of leakage of hydraulic fluid from the system. With a perfectly tight system and absolutely no fluid loss through leakage, pistons 48 and 50 would never need to be any farther apart than the distance necessary to displace precisely the volume displaced by the piston rod 14, namely the aforesaid predetermined amount. However, as fluid is lost through leakage, pistons 43 and 50 will gradually drift apart and eventually, the system must be recharged with fluid from the reservoir.

It will be apparent from the foregoing to those "killed in the art that this invention provides a simple, efficient, and inexpensive closed hydraulic system, and that this system permits volume variations by one element thereof because of the compensator which is capable of producing volume when pressure in a conduit falls below pump supply pressure and is capable of taking on volume if the pressure goes above that supply pressure. Other advantages will be apparent to those skilled in the art.

What is claimed is:

1. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid and discharging a different volume of fluid, the different volume being smaller than said given volume by a predetermined amount, and movable through said cycle in the opposite direction while receiving said smaller volume of fluid and discharging said given volume of fluid; a reversible pump having a pair of ports and operable in either direction, the rate of fluid flow through one port being equal to the rate of fluid flow through the other port at any given instant; conduit means connecting the pump ports with the motor; and a double-acting expansible chamber device, open at all times to both pump ports through the conduit means, to maintain under a supply pressure whichever pump port is passing fluid into the pump and to supply or receive said predetermined amount of fluid volume'to or from the conduit means according to need.

2. A hydraulic system comprising: a cylinder and piston mechanism having a head end and a rod end and forming a motor of Which the piston is movable through a working stroke in one direction while the cylinder is receiving a given volume of fluid at its head end and discharging a different volume of fluid from its rod end, the different volume being smaller than the given volume by a predetermined amount determined in part at least by the size of the piston rod, and movable through said stroke in the opposite direction while the cylinder is receiving said smaller volume of fluid at its rod end and discharging said given volume of fluid from its head end; a source of hydraulic fluid under pressure, said source supplying and receiving fluid at equal rates for any given set of operating conditions; conduit means connecting the source with the cylinder; and a double-acting expansible chamber device having a two-part cylinder of which opposite ends are connected with the conduit means, stop means between the ends of the cylinder, a piston in eachpart of the cylinder movable between the stop means and a cylinder end, and yieldable means biasing the pistons apart, whereby said device maintains a supply pressure on whichever conduit portion is passingfiuid into the source and supplies or receives said predetermined amount of fluid volume to or from the conduit means according to need.

3. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid, the different volume being smaller than said given volume by a predetermined amount, and movable through said cycle in the opposite direction while receiving said smaller volume of fluid and discharging said given volume of fluid; a reversible pump having a pair of ports and operable in either direction, the rate of fluid flow through one port being equal to the rate of fluid flow through the other port at any given instant; conduit means connecting the pump ports with the motor; and a doubleacting expansible chamber device having a two-part cylinder of which opposite ends are connected with the conduit means, stop means between the ends of the cylinder, a piston in each part of the cylinder movable between the stop means and a cylinder end, and yieldable means biasing the pistons apart, whereby said device maintains a supply pressure on whichever pump port is passing fluid into the pump and supplies or receives said predetermined amount of fluid volume to or from the conduit means according to need.

4. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid and discharging a different volume of fluid, the different volume 'being smaller than said given volume by a predetermined amount, and movable through said cycle in the opposite direction while receiving said smaller volume of fluid and discharging said given volume of fluid; a reversible pump having a pair of ports and operable in either direction, the rate of fluid flow through one port being equal to the rate of fluid flow through the other port at any given instant; conduit means connecting the pump ports with the motor; and an expansible chamber device having a two-part cylinder of which opposite ends are connected with the conduit means, stop means between the two parts of the cylinder and to which the two parts are joined, a piston in each part of the cylinder and movable between the stop means and the outer end of its associated part, and yielda-ble means between the pistons and biasing them outward whereby said device produces volume if the pressure in a connected portion of the conduit means falls below the supply pressure of the pump, and takes on volume if the pressure goes higher than the supply pressure.

5. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid and discharging a different volume of fluid smaller than said given volume, and movable through said cycle in the opposite direction While receiving said smaller volume of fluid and discharging said given volume of fluid; a reversible pump having a pair of ports and operable in either direction, the rate of fluid flow through one port being equal to the rate of fluid flow through the other port at any given instant; conduit means connecting the pump ports with the motor; and means connected with and at all times open to both pump ports and capable of producing volume if the pressure in the conduit means falls below the pump supply pressure and capable of taking on volume when the pressure in the conduit means goes higher than pump supply pressure.

6. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid and discharging a different volume of fluid, the diiferent volume being smaller than said given volume by a predetermined amount, and movable through said cycle in the opposite direction while receiving said smaller volume of fluid and discharging said given volume of fluid; a source of hydraulic fluid under pressure, said source supplying and receiving fluid at equal rates for any given set of operating conditions; conduit means connecting the source with the motor; and means connected with and at all times open to both pump ports and capable of producing said predetermined amount of volume if the pressure in the conduit means falls below the source supply pressure and capable of taking on volume when the pressure in the conduit means goes higher than source supply pressure.

7. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid and discharging a different volume of fluid smaller than said given volume, and movable through said cycle in the opposite direction while receiving said smaller volume of fluid and discharging said given volume of fluid; a source of hydraulic fluid under pressure, said source supplying and receiving fluid at equal rates under any given operating conditions; conduit means con necting the source with the motor; and means, including a double-acting cylinder having a stop between the ends and a pair of pistons provided with means to bias them apart and movable between the stop and a cylinder end, capable of producing volume if the pressure in the conduit means falls below the source supply pressure and capable of taking on volume when the pressure in the conduit means goes higher than source supply pressure.

8. A hydraulic system comprising: a cylinder and piston mechanism having a head end and a rod end and forming a motor of which the piston is movable through a working stroke in one direction while the cylinder is receiving a given volume of fluid at its head end and discharging a different volume of fluid from its rod end, and movable through said stroke in the opposite direction while the cylinder is receiving said smaller volume of fluid at its rod end and discharging said given volume of fluid from its head end; a source of supply of hydraulic fluid under pressure which supplies and. receives fluid at equal rates; conduit means connected with and at all times open to both pump ports and connecting the source with. the cylinder; and means capable of producing volume if the pressure in the conduit means falls below the supply pressure and capable of taking on volume when the pressure in the conduit means goes higher than supply pressure.

9. A hydraulic system comprising: a cylinder and piston mechanism having a head end and a rod end and forming a motor of which the piston is movablethrough a working stroke in one direction while the cylinder is receiving a given volume of fluid at its head end and discharging a different volume of fluid from its rod end, the different volume being smaller than the given volume by a predetermined amount determined in part at least by the size of the piston rod, and movable through said stroke in the opposite direction while the cylinder is receiving said smaller volume of fluid at its rod end and discharging said given volume of fluid from its head end; a source of supply of fluid under pressure which supplies and receives fluid at equal rates; conduit means connecting the source with the cylinder; and means connected with and at all times open to both pump ports and capable of producing said predetermined amount of volume if the pressure in the conduit means falls below the supply pressure and capable of taking on volume when the pressure in the conduit means goes higher than supply pressure.

10. A hydraulic system comprising: a motor movable through a given cycle in one direction while receiving a given volume of fluid and discharging a different volume of fluid smaller than said given volume, and movable through said cycle in the opposite direction while receiving said smaller volume of fluid and discharging said given volume of fluid; a source of hydraulic fluid under pressure, said source delivering and receiving fluid at equal rates for given operating speeds; conduit means connecting the source with the motor; and means connected v 7 with and at all times open to both pump ports and capable of producing volume if the pressure in the conduit means falls below the source supply pressure and capable of taking on volume when the pressure in the conduit means goes higher than source supply pressure.

UNITED, STATES PATENTS Williams Dec. 17, 1912 Danna u June 8, 1920 Sanford June 27', 1939 Kremiller Feb. 17, 1948 Huflerd Sept. 14, 1948 Herrstrum Feb. 14, 1950 

